The fullerene structure, identified experimentally for carbon was given theoretical consideration here to a number of silicone clusters. Also, compact-type structures, containing no voids, were considered as an alternative. MINDO/3 approximation and Monte Carlo algorithm are used for numerical optimization of cluster structures.

The study of Si_n and Si_nH_n fullerene structures with sizes 20<n<60 shows stability of spheroidal silicon clusters with more than 36 Si atoms involved. At sp2 hybridization of silicon atoms, which is typical for relatively large spheroidal clusters, the binding energy(BE)/atom:
exhibits a general fast increasing function with increasing number of atoms. On the contrary, the clusters of small sizes ( n < 32 ) were much deformed by the optimization procedure.

Unstable hollow cluster Si20 deformed after optimization. The saturation with hydrogen provides again the regular fullerene form of Si20H20.

Spheroidal clusters resulting from the Monte Carlo simulations were hydrogenated, then MC procedure was used again for geometry optimization.  Saturation of dangling bonds of strongly distorted unstable fullerene structures of small sizes with H atoms followed by geometry optimization, yields stable spheroidal Si_nH_n structures surpassing the alternative hydrogenated compact clusters in binding energy.

Optimization of compact tetragonal cluster Si45 is initiated with four H atoms inserted. Hollow-type

The function: is used as a simple energetic description of Si_nH_n clusters. In contrast to Si_n clusters, the function was found to be descendent for hydrogenated clusters containing more than 36 Si atoms. The calculation shows that at n>50 the compact structure of Si_nH_n clusters is more preferable.